Integrated circuits are operating at ever increasing speeds. For example, integrated circuits for markets such as communication and storage are often embedded with multiple cores that send and receive signals at speeds greater than about two and one-half gigabits per second, which is defined herein to be a high speed signal or a high speed device.
As the term is used herein, “integrated circuit” includes devices such as those formed on monolithic semiconducting substrates, such as those formed of group IV materials like silicon or germanium, or group III-V compounds like gallium arsenide, or mixtures of such materials. The term includes all types of devices formed, such as memory and logic, and all designs of such devices, such as MOS and bipolar.
Integrated circuits are typically formed into packaged devices with a package substrate. The package substrate provides all of the electrical connections to the integrated circuit, and provides separate electrical connections to another structure, typically referred to as the printed circuit board. Thus, as the terms are used herein, there are three different structure types used in an electrical circuit, which structures are the integrated circuit, the printed circuit board, and the interface between the integrated circuit and the printed circuit board, which is the package substrate. As contemplated herein, the integrated circuit does not at any time physically contact the printed circuit board, and the printed circuit board and the package substrate are physically separate elements that are manufactured at different times and using different processes.
The distinction between the printed circuit board and the package substrate is further exemplified by the time at which they are electrically connected to the integrated circuit. The package substrate is considered to be a part of the packaged integrated circuit, and the integrated circuit is typically not shipped from the integrated circuit manufacturer until it is assembled as a packaged device with the package substrate. However, the packaged substrate is typically assembled with the printed circuit board in a different facility at a later time by a purchaser of the packed integrated circuit. Thus, one skilled in the art is able to quickly distinguish between a printed circuit board and a package substrate.
For high speed integrated circuits, isolation within the transmitter and receiver pairs of the high speed signals and between the high speed signals and the other signals in the integrated circuit, package substrate, and printed circuit board are becoming a critical factor for ensuring the proper performance of the system. As a result, package designers strive to route integrated circuits so that the high speed signals are adequately isolated in the package substrate, and at the same time the package substrate design allows for adequate isolation in the printed circuit board. In addition, the package substrate design preferably enables routing of the high speed signals in the lowest possible number of printed circuit board layers, since this is a direct contributor to the overall cost of the system.
What is needed, therefore, is a system of routing high speed signals in a manner that overcomes problems and achieves goals, such as those described above, at least in part.